Layering SPF products isn't necessarily good — here's what to do instead

This is because layering SPF products doesn't increase the number of active ingredients.

It does, however, increase your chances of getting the right amount of sunscreen on your face.

It may be September, but the sun is still out and strong as ever. Your first instinct may be to reach for all products containing SPF — sunscreen, lotion, makeup — and layer them in order to get maximum coverage. Slathering on SPF 15 moisturizer, then SPF 30 sunscreen, and then SPF 20 foundation should give you a total SPF of 65, right? Unfortunately, that's not the case.

"Sunscreens work by basically limiting the amount of UV rays that get to your skin, but the limit is based on the highest number of the SPF that you are using, not the additive number," Dermatologist Michael Kassardjian told INSIDER.

More products don't equal more coverage

Stick to a high SPF and reapply often. Sarah Schmalbruch/INSIDER

Feeling confused? Papri Sarkar, a dermatologist in Massachusetts, told INSIDER that it's a very common misconception among her patients.

"All of our life we're taught that one apple plus one apple equals two apples," she said. "Intuitively you should be able to get an additive effect." But this is not the case when it comes to SPF.

"SPF measures how much of the sun's UVB rays are blocked, but layering products doesn't improve the amount of active ingredients in the cream," she explained. "The only way to change the SPF is to change the amount of active ingredients within the formulation. Applying more on top doesn't add any extra coverage."

So if you were to layer up the lotion with SPF 15, the sunscreen with SPF 30, and the foundation with SPF 20, your total SPF would only be 30. The highest SPF number would be your overall protection from the sun. But before you think that buying all those SPF products was a total waste, both Kassardjian and Sarkar said that there is a hidden benefit to using all those different products.

It might ensure you apply the right amount of sunscreen

"Pretty much nobody applies as much sunscreen as you're supposed to," Sarkar said. "Studies have found that people use anywhere from one-fourth to one-half of the amount of sunscreen that they're supposed to apply to get the full SPF coverage that's listed on their sunscreen bottle. Layering different products with sunscreen is a great idea in the sense that you'll actually be getting the amount of sunscreen you think you are."

Kassardjian agreed with Sarkar, and added that you'll also be less likely to miss a spot on your face (like your neck, your ears, or your eyelids) if you apply multiple SPF products.

Kassardjian explained that it's best to use actual sunscreen (with a minimum SPF of 30), as relying solely on SPF in makeup can cause trouble.

"Although your makeup may state it has a certain amount of SPF, it is not typically applied thick enough to get that SPF result," he explained. "Additionally, the SPF ingredients in makeup are usually chemical blockers and not physical blockers. Chemical blockers are generally thinner, absorbed more quickly, and degraded faster with sun exposure."

Here's how to properly apply sunscreen

Reapply every two hours if you're getting wet or sweating. Seth Wenig/AP

To get the most out of sunscreen application, Kassardjian told INSIDER that you should apply it onto clean, dry skin 30 minutes prior to going outside.

Sarkar added that you should reapply every two hours if you're sweating or every four to six hours if you're not. "Another option instead of using sunscreen is to use sun-protective clothing like hats, shirts, or sunglasses," she said. "Luckily, you don't need to reapply them, they never wear off, and they're better protection than a sunscreen."

Kassardjian also said that powder sunscreen is an effective alternative for reapplication if someone has makeup on and is unable to wash their face before reapplying sunscreen.

So, no, layering sunscreen won't help you achieve a super high SPF number. But it will help you get enough actual sunscreen on your face — something we all could benefit from — which will protect you from sun damage. In the market for a new broad-spectrum sunscreen? Check out our favorites here. Just be sure to reapply every couple of hours, and you'll be good to go.